Field of the Invention
The present invention relates to the preparation of a condensation product of 1-amino-2-propanol and formaldehyde, the condensation product, the use thereof for reducing the amount of hydrogen sulphide in liquids and gases and also a corresponding process.
Hydrogen sulphide (H2S) is an unpleasantly smelling, toxic gas which poses a great hazard to health and leads to severe corrosion phenomena in industrial plants. Lawmakers have therefore imposed strict obligations for reducing the H2S content.
Description of the Related Art
WO 02/051968 A1 discloses a process for reducing the amount of hydrogen sulphide in a liquid or a gas by treatment with an H2S-scavenging product. The H2S-scavenging product is obtained by reaction of i) a compound having a carbonyl group with ii) an alcohol, thiol, amide, thioamide, urea or thiourea. The product is preferably prepared by reaction of formaldehyde with amine-free alcohol or urea. An example of an amine-free alcohol is ethylene glycol. The H2S-scavenging agent can optionally be used together with an amine, in particular N-(2-hydroxy ethyl) amine (ethanolamine).
WO 98/02501 discloses that bis(oxazolidine) derivatives can be used as scavenging agents for sulphur compounds. An example of a bisoxazolidine is 3,3′-methylenebis(5-methyloxazolidine), which is obtained by reaction of 1-amino-2-propanol (2-hydroxypropylamine, monoisopropanolamine, MIPA) with formaldehyde in a molar ratio of 2:3 (i.e. 1:1.5). The anhydrous condensation product Grotan® OX (3,3′-methylenebis[5-methyloxazolidine]) from Schülke & Mayr GmbH, Norderstedt, Federal Republic of Germany, displays good effectiveness in the chemical neutralization of H2S.
However, it is known from various formaldehyde depot compounds used, for example, for preserving water-based products and processes that they tend to liberate formaldehyde into the gas phase and accordingly produce an unpleasant smell and also lead to instability or a neck-in effect.
According to DE 197 22 858 A1, compositions based on iodopropynyl butylcarbamate and formaldehyde depot compounds are used as preservatives. The addition of particular glycols, preferably 1,2-propylene glycol, has a positive influence on the odour of the compositions and reduces the emission of volatile materials (such as formaldehyde).
DE 102 44 442 A1 discloses a preservative which has reduced formaldehyde emission and contains a) at least one formal and b) at least one emission-reducing additive selected from among urea, urea derivatives, amino acids, guanidine and guanidine derivatives.
The preservatives according to DE 10 2004 014 447 A1 comprise a) at least N-formal, b) at least one emission-reducing additive and c) monoethylene glycol.
The product Grotan® WS (Schülke & Mayr GmbH, Norderstedt, Federal Republic of Germany) is a water-containing product which contains about 80% by weight of the formaldehyde depot compound α,α′,α″-trimethyl-1,3,5-triazine-1,3,5-(2H,4H,6H)-triethanol (N,N′,N″-tris(2-hydroxpropyl)hexahydrotriazine, hereinafter TTT). TTT is prepared by condensation of MIPA with formaldehyde (in a molar ratio of 1:1). The condensation product is a colourless to yellow liquid which is storage-stable and will keep for more than 36 months, but has an undesirably high viscosity, especially at low temperature. Aqueous dilutions of Grotan® WS, in contrast, are not storage-stable.
According to the teaching of EP 0 347 815 A2, alkanolamines are used for stabilizing triazine derivatives. Here, the additional presence of surfactants is said to be absolutely necessary. However, the surfactants used in the examples have poor biodegradability.
DE 27 11 106 A1 discloses a process for preparing bis(5,5′-dimethyl-1,3-oxazolidin-3-yl)methane, in which 1-amino-2-propanol is reacted with an excess of for-maldehyde at elevated temperature.
DD 229 707 A1 describes a process in which alkanolamine and formaldehyde are firstly reacted with one another at a temperature in the range from 30° C. to 80° C., with it being possible to employ a stoichiometric excess of alkanolamine to increase the functionality. The products obtained after further addition of alkali metal hydroxide and reaction with alkylene oxide are used as pharmaceuticals, insecticidally or fungicidally active sub-stances or as additives for lubricating greases.
DE 26 35 389 C2 discloses preservatives and disinfectants based on condensation products of amino alcohol or amino thiol with formaldehyde. Furthermore, it is stated that an excess of formaldehyde can also be used, but this does not participate in the reaction but instead remains as free formaldehyde in the reaction mixture. The preservatives and disinfectants are suitable for aqueous paints, cooling lubricants and adhesive solutions, or for preserving cooling water circuits or water circuits in paper production.
WO 97/25126 A2 describes compositions for removing sulphides from gas streams and a corresponding regenerative process. In the process, the gas stream is brought into contact with an H2S-scavenging agent, an inorganic ion and an oxidation catalyst. Examples of H2S-scavenging agents are 3,3′-methylenebisoxazolidine and 1,3,5-triazine-1,3,5-(2H,4H,6H)triethanol (N,N′,N″-tris(2-hydroxyethyl)hexahydrotriazine), the reaction product of monoethanolamine with formaldehyde in a molar ratio of 1:1.
WO 90/07467 A1 describes a process for selectively reducing the contents of hydrogen sulphide and organic sulphides in gaseous and/or liquid hydrocarbon streams or non-hydrocarbon streams, in which the streams are brought into contact with compositions which comprise the reaction product of (i) a lower alkanolamine with (ii) a lower aldehyde. An example of a lower alkanolamine is monoethanolamine, and an example of a lower aldehyde is formaldehyde.
WO 96/05907 A1 describes a process for reducing H2S in liquid and gaseous streams, which is characterized in that the streams are contacted with a condensation product of dialdehyde and alkanolamine. Preference is given to condensation products of glyoxal and monoethanolamine.
WO 94/08980 A1 discloses hexahydrotriazines having at least one alkoxyalkylene group and the use thereof as H2S scavengers.
US 2003/0234383 A1 proposes reacting the mixture of ethanolamine and diglycol amine with formaldehyde in order to produce an H2S-scavenging agent, and in order to prevent crystalline dithiazine deposits. According to U.S. Pat. No. 8,512,449 B1, an aqueous mixture containing triazine, glycol ether and alcohol is used for scavenging sulphide.
WO2013/101361 A1 proposes using the product of the condensation of aldehyde with a secondary amine in order to scavenge H2S.
DE 10 2012 203 003 A1 discloses liquid preparations for reducing free oxygen and preserving water. The preparations contain at least one N-formal and at least one dialkylhydroxylamine.
WO 2016/105341 A1 states that the use of triazine compounds for removing sulphur compounds leads to an undesirably high pH and to deposits, and instead proposes using combinations of i) an aldehyde-free compound (for example acrylate, acrylonitrile, ethyl trans-4-oxo-2-butenoate, para-benzoquinone or ortho-benzoquinone) with ii) a weak base (for example amine).